HepG2 cells were treated or untreated with Na-Butyrate and Chromatin immunoprecipitations were performed in order to investigate the genomic regions displaying changes in histone acetylation pattern (H3ac and H4ac) after treatment. Such ChIPs material were analyzed by ChIP-Chip, hybridizing ChIP DNA and reference DNA into arrays covering 1% of the human genomes as defined by the ENCODE consortium. By comparing arrays hybridized with ChIPs obtained using antibodies against acetylated histones before and after butyrate treatment, we deteceted those genomic regions that significantly changed in their histone acetylation patterns. Furthermore, as a control in order to determine specific enrichemnts we performed ChIPs where no antibody was used and hybridized the resultsing DNA against reference DNA. In this last case, experiments were performed only with untreated cells.